The use of enzymes derived from microbial cells to effect specific chemical transformations is well-known. In carrying out such transformations, the cell-free enzyme preparation, ruptured cells or whole cells can be efficiently used as the source of biocatalyst. The free enzymes or cells can be efficiently used in batch-type processes but do not lend themselves to continuous industrial scale operations. For example, in the conversion of glucose to fructose catalyzed by glucose isomerase or the conversion of sucrose to palatinose catalyzed by sucrose mutase, economically competitive processing requires that the substrate solution (glucose or sucrose) be passed over and through a fixed bed of the biocatalyst with continuous recovery of the product of the conversion. This processing technique has led to increased interest in the preparation of various forms of immobilized biocatalysts.
For example, Gestrelius discloses in U.S. Pat. No. 4,288,552 the use of polyethylenimine and glutaraldehyde for the immobilization of glutaraldehyde sensitive enzymes. An improvement to this method is disclosed in U.S. Pat. No. 4,355,105 wherein intracellular enzymes not sensitive to glutaraldehyde are immobilized by first being contacted with glutaraldehyde and then introducing polyethylenimine to the reaction medium. In U.S. Pat. No. 4,167,447 there is disclosed a method for the immobilization of enzymes which involves mixing an aqueous solution of an enzyme with chitosan dissolved in water at pH 3-7 to form a product which can be precipitated by the addition of an alkali or a source of sulfate ions. In another embodiment of the process disclosed in this patent, solid chitosan is cross-linked with a polyfunctional cross-linking agent such as a dialdehyde and then contacted with an aqueous solution of an enzyme. Muzzarelli discloses the immobilization of enzymes, including glucose isomerase, on chitin and chitosan in Enzyme Microb. Technol., 1980, Vol. 2, July 1977. In Japanese Kokai Pat. No. Sho 51 [1976]-128, 474 a glucose isomerase immobilization method which involves the blending of glucose isomerase producing bacteria and chitosan with subsequent treatment with a polyaldehyde is disclosed. In U.S. Pat. No. 4,094,743 there is described a process in which an enzymatically active product insoluble in aqueous medium is prepared by treating chitosan as an inert support with a dialdehyde after which an enzyme is fixed to the support thus treated.
Co-pending U.S. application Ser. No. 467,851 (filed Feb. 24, 1983), now U.S. Pat. No. 4,543,332, claims the immobilization of biocatalysts using a polyamine flocculating agent and cross-linking agent with the subsequent spheronization of the immobilized product using a spheronizing device consisting of a milled friction plate as rotor situated in a cylinder such that the cylinder provides a stationary side wall for the plate while allowing it freedom to rotate. In German AS 21 37 042 there is described a method for the spheronization of enzyme compositions, particularly those which are useful in the detergent industry. The device used for such spheronization is similar to that described in the aforementioned '851 application.
In U.S. Pat. No. 4,283,496 there is disclosed a method for the conversion of glucose to fructose which involves the use of an enzyme produced by an organism from the species flavobacterium arborescens.